broken button

Hello There ! I am very sorry to know you are having such conveniences. We highly recommend going over the steps mentioned on the links bellow :

Troubleshoot issues with an Xbox Wireless Controller | Xbox Support

Troubleshoot your Xbox Wireless Controller | Xbox Support

If that didn't resolve your issue you will have to repair it. Access The link bellow to request a repair for your controller :

Getting your Xbox device serviced | Xbox Support

If you are unable to create the order on that link please contact our live support:

Contact us | Xbox Support

Hardly because you can't know the extent of the damage or if you burned some kind of contact, only assistance could help you.

Hello, first it's a pleasure to be able to help you today.

My name is welcome to the community.

Hello Ewan, if you spilled some kind of liquid as you mention in your description it damaged the contacts of your controller buttons.

You will have to check your control's guarantee to see if it is still valid, if not, the ideal thing would be to send the control to some technical assistance that can help you.

https://support.microsoft.com/devices

You will need to contact support directly for assistance with that. You will probably need the receipt when you contact them so be sure to have it available. support.xbox.com/.../contact-us

Keep us updated on your progress. Good Luck!!

would personally reset the whole console and see if this helps, if not successful check if controller is in warranty and get a replacement